The present invention relates to a method of manufacturing aluminum frames for photomask protective films and particularly a method capable of manufacturing aluminum frames for photomask protective films with less chuck setups and simpler machining processes.
Semiconductors and integrated circuits are widely used in people""s life and work nowadays. For instance, they play critical roles in personal computers, cars, mobile phones, satellite communications, and household appliances.
Integrated circuits are clusters of specific electric circuits shrunk and built on a size about or smaller than 2 cm2, and each contains thousands of individual solid state electronic elements that are visible only through microscopes. The solid state electronic elements also are called microelectronic elements.
Manufacturing of integrated circuits generally can be divided in three stages: 1. Manufacturing silicon chips; 2. Manufacturing integrated circuits; 3. Packaging the integrated circuits. Individual manufacturing processes include physical evaporation depositing, chemical evaporation depositing, micro photolithography, etching, diffusion, ion planting, oxidizing, heat treatment, etc. The micro photolithography is a critical process. The process includes coating a layer of photosensitive material on the chip surface, and projecting a parallel light through a photomask made of glass to the photosensitive material. The photomask has opaque patterns to block the light to allow the photosensitive material on the chip surface having selective exposure to form desired patterns on the photosensitive material on the chip surface. This is also called xe2x80x9cexposingxe2x80x9d process. The tools required to form the desired exposing patterns on the chip surface, besides the light source, also include a photomask for transferring the patterns. During the exposing process, in order to prevent dust from smearing the photomask and contaminate photosensitive material for the circuit pattern on the chip surface, the photomask usually is supported by an aluminum frame and bonded to a protective film on the surface. Through this setup, dust pollution and contamination on the pattern transfer can be minimized.
FIG. 1 shows a conventional aluminum frame for a photomask protective film. It has an aluminum frame 10 with a lower surface coating with adhesive for bonding a photomask 11. The upper surface of the aluminum frame 10 also is coated with adhesive for bonding a protective film 12. During exposing process, dust and debris 13 will fall on the protective film 12 without directly hitting the photomask 11, hence pattern transfer during exposing process will have minimum impact.
FIG. 2A illustrates a conventional machining method for fabricating the aluminum frames for photomask protective films. The method includes: stacking and positioning a plurality of aluminum sheets 20 (three layers have been shown in the drawing as an example) together; drilling selected number of holes through the aluminum sheets 20 (the hole number is dependent on the size of the aluminum sheet, usually four) for housing screw bolts 21 to fasten the aluminum sheets 20 to a base 22 of a machine tool to prevent the aluminum sheets from moving or dislocating during machining operations. The outer peripheral rims of the aluminum sheets 20 also are clamped by chucks 23 to hold the aluminum sheets 20 steadily and securely on the base 22.
Referring to FIG. 2B, during conventional machining processes, the aluminum sheets 20 (three layers in this example) are fastened to the base 22 of the machine tool, then a milling cutter 25 is deployed to perform milling operation along a selected path reciprocally. When the milling depth and profile have reached the required dimensions, dismantle the fastening screw bolts 24 and remove the chucks 23 to get the finished aluminum frames 10. Then disengage the screw bolts 21 to remove the remnant aluminum material 26. The finished aluminum frames 10 still need some other machining operations such as surface grinding and forming chamfer angles.
The machining method set forth above has a number of advantages:
1. Each aluminum sheet has to be aligned and drilled before milling operation, thus increasing the processing complexity.
2. While using screw bolts can increase fastening steadiness, it also takes more time and efforts to fasten and dismantle the screw bolts.
3. After milling operation, the aluminum frame still need surface grinding and chamfering processes, this requires additional fastening and machining operations.
This further increases production costs.
4. The center portion of the aluminum sheet is useless and becomes a waste after machining processes.
In view of aforesaid disadvantages, the primary object of the invention is to provide an improved method of manufacturing aluminum frames for photomask protective films that require less chucks and screw bolts setup time, and has simpler machining processes thereby to achieve better production efficiency and save production costs.
Another object of the invention is to provide hollow aluminum material for machining to reduce excessive remnant of aluminum material.
To attain the foregoing objects, the method of the invention includes the steps of: selecting a square and strut-shaped aluminum material (solid or hollow), fastening the selected aluminum material to a base of a machine tool, milling the aluminum material to form a hollow trough with a selected depth according to required specifications and dimensions of the aluminum frame for forming a plurality of aluminum frames for photomask protective films, using a milling cutter which has multiple sloped chamfer surfaces to mill the hollow aluminum strut to become multiple layers with chamfer angles, using a cutter to cut off the aluminum strut at the perimeter to form an individual aluminum frame of a selected height, and grinding the cross section of the remaining hollow aluminum strut with a grinding tool, and separating and forming a plurality of individual aluminum frames from the aluminum strut by repeating the cutting and grinding processes.
In an embodiment of the invention, a solid or hollow aluminum square-shaped strut may be used for machining. When a hollow aluminum strut is being chosen, it has adequate thickness to withstand machining operations. The height of the aluminum strut is based on space limitation and steady requirements of machining. The bottom end of the aluminum strut may be drilled with a plurality of holes and taping with screw threads for fastening inversely to the base of the machine tool. Fastening the aluminum strut by chucks as the conventional techniques may also be adopted.
When the aluminum material is fastened to the milling machine or programmable center machine tool, milling cutters may be used to fabricate the outer and inner side of the aluminum material to a selected depth depending on the length of the cutters and machining steadiness requirements. When the outer dimensions are finished, use a special-made milling cutter for further machining. The special-made milling cutter has a plurality of spaced chamfer sloped surfaces formed axially with the interval of two neighboring sloped surfaces equal to the thickness of the aluminum frame. Hence the milling cutter may be used to cut the outer and inner side of the hollow strut to form layers of individual aluminum frames with desired chamfer angles.
After completing the foregoing processes, mount a server cutter to the machine tool such as a slitting cutter, an abrasive cutting wheel, or a saw to move around the periphery of the aluminum material to sever and form an individual aluminum frame. When a first aluminum frame is separated from the aluminum strut, use a grinding tool to grind the remaining cutting edge on the top end of the strut then sever a second aluminum frame. Repeat the processes to produce the aluminum frames until the aluminum strut is exhausted.